Currently, wood deck stains are comprised of resinous, film-forming coatings which lay on the surface of wood to create a protective barrier to weathering, physical wear, and UV degradation. These coatings have traditionally been based on alkyd enamels, acrylic, and urethane resin-lacquer technology. More recently, water-based versions of these technologies have become common. These resinous approaches do not penetrate deep into the wood, rather, they lay on the surface of the wood forming a resinous film where they are prone to blistering, peeling, and flaking. This limits their durability significantly. The focus has been to improve upon the UV stability of resinous film-forming coatings, but lack of deep penetration of the coatings into the wood substrate has thwarted performance improvements to long-term durability.
The average homeowner will spend thousands of dollars installing and maintaining exterior structures. In particular, the treatment, beautification, and protection of exterior structures, including, but not limited to wooden decks, wooden siding, wooden shutters, wooden shingles, wooden flooring and laminates, synthetic decking, and synthetic wood is not only desirable from an aesthetic point of view, but is necessary to ward off damage imparted to wood and other porous substrates from exposure to physical, biological, and chemical attacks.
It is well known through investigative studies performed by the United States Department of Agriculture's Forestry Products Division (USDA FP Div.) that exterior wooden surfaces are composed of structurally dynamic materials which react directly to the immediate surrounding environment. These structurally dynamic materials have been identified to be the most significant factor contributing to the failure of film-forming exterior paints/coatings/stains on exterior wooden surfaces. Simply stated, exterior wood expands and contracts in reaction to changes in humidity and temperature, making long term adhesion of currently available protective film-forming finishes difficult, if not impossible.
Furthermore, exposed (untreated) exterior wooden structures are susceptible to rot and/or discoloration. This discoloration is typically caused by fungal infection, bacterial infection, and/or UV damage from natural sunlight, and is aggravated by damage caused by seasonal and daily temperature changes. If a fungus or fungi does not infest the substrate, it may, at the least, cause discoloration. Contributing factors to exterior wood discoloration include: (1) fungal infestation of porous surface and sub-surface structures, (2) potential fungal/bacterial digestive damage on the wood itself, and (3) UV damage to the wooden surface which, with rain, may wash away surface layers of wood, thus exposing further wood to UV damage and renewing fungal nutrients and favorable conditions for fungal infestation.
Wood is comprised of three primary ‘building block’ materials: lignin, cellulose, and hemicellulose. Research results from the USDA FP Div. report that the lignin and related phenolic resin components of wood are most susceptible to UV damage due to chromophore absorbance of UV light. Lignin acts as the primary binder that maintains the structural integrity of wood. UV damage of lignin causes discoloration and the eventual erosion of wood cells and fiber thereof. Polyphenolic compounds cause the lignin matrix to “break down” and be removed by the leaching action of water.
USDA investigation has also revealed that solvents and water components used in wood sealers, preservatives, and stains cause specific structures in wood that control water transport to inhibit the penetration of wood sealers, preservatives, and stains into the wood. These structures effectively act as ‘valves’ that open and close to control the flow of sap and water from the roots to the leaves in trees. These ‘valves’ have been shown by the USDA to still be responsive to water and solvents well after the harvesting and processing of the tree. The continued activity of these liquid-transport, controlling structures contributes to the dynamic nature of wood in direct response to ambient temperature and humidity levels.